Optical filter

ABSTRACT

An optical filter for absorption of electromagnetic radiation of wavelength 532×10 -9  m with excellent photostability properties is provided by a polymeric host material such as polycarbonate incorporating the absorbing compound 5, 10, 15, 20 tetrakis (4-methoxyphenyl)-21H,23H porphine palladium (II).

BACKGROUND OF THE INVENTION

This invention relates to an optical filter for the absorption ofelectromagnetic radiation. More particularly it relates to an opticalfilter for the absorption of electromagnetic radiation having awavelength in the region of 532×10⁻⁹ m whilst allowing transmission ofthe remaining electromagnetic radiation.

In certain circumstances it is desirable to absorb electromagneticradiation in a narrow wavelength band by means of an optical filterwhilst allowing transmission of a substantial portion of the incidentradiation, i.e. that at other wavelengths. In situations where laserradiation i.e. coherent radiation of a defined wavelength, is employed,such as certain medical and industrial applications, the beam ofradiation may contact the eye or other device and cause damage thereto.In these situations absorption of electromagnetic radiation over thenarrow wavelength band corresponding to the wavelength of the radiationemitted by the laser is necessary to protect the eye or optical device.Conventionally this has been achieved by way of an optical filter whichwhilst absorbing the narrow wavelength band corresponding to thewavelength of the laser, transmits the substantial portion of theincident radiation i.e. that at other wavelengths. Such optical filtersare commonly manufactured by incorporating a compound which hasparticular absorption characteristics into a suitable host material, forexample a polymeric matrix such as polycarbonate.

U.S. Pat. No. 4,622,174 discloses a transparent protective laser shieldcomprising a transparent host material and having at least onechromophore incorporated therein. The or each chromophore is selectedfrom a porphyrin complex which has been modified by a metal, soproviding metallo porphyrin complexes in the transparent material whichabsorb optical radiation of a pre-determined narrow wavelength bandlocated within a selected broad wavelength band passed by thetransparent host material. In particular, platinum octaethylporphyrin(PtOEP) is disclosed as being particularly suitable for absorption ofneodymium YAG--doubled laser radiation at 532×10⁻⁹ m. Although PtOEPabsorbs strongly at 532×10⁻⁹ m, its properties of photostability arevery poor and unsuitable for a number of applications.

U.S. Pat. No. 4,657,345 discloses a similar shield in which theabsorbers are diffused into a host material adjacent to its surfacerather than being disseminated uniformly through it.

UK Patent Application No. 2225445 discloses a similar type of opticalfilter in which platinum deuteroporphyrin IX dimethyl ester isincorporated into the host as the absorbing material. This absorber hasan absorption maxima at 533×10⁻⁹ m.

In each of the above-mentioned documents platinum is used to form themetallo porphyrin complex in the absorbing material and consequently theabsorbing material is relatively expensive.

SUMMARY OF THE INVENTION

The present invention is concerned with providing an optical filterwhich absorbs strongly at 532×10⁻⁹ m.

Furthermore the present invention aims to provide an optical filterwhich is relatively inexpensive to manufacture.

According to an aspect of the present invention there is provided anoptical filter for the absorption of electromagnetic radiation in anarrow wavelength band, the filter comprising a transparent hostmaterial, and an electromagnetic radiation absorbing material comprisingthe compound 5,10,15,20 tetrakis (4-methoxyphenyl)-21H,23H porphinepalladium (II).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a preferred embodiment of the invention the transparent host materialcomprises a polymeric matrix, preferably polycarbonate.

As the cost of palladium is almost a quarter that of platinum, opticalfilters according to the present invention are considerably lessexpensive than those which incorporate platinum.

An embodiment of the invention will now be described.

The compound 5,10,15,20 tetrakis (4-methoxyphenyl)-21H,23H porphinepalladium (II) [TTL], was synthesized in the manner described in theJournal of American Chemical Society, Vol 81, 1959 pages 5111 to 5119,the disclosures of which are incorporated herein by way of reference.

The TTL compound is mixed as a dry powder with polycarbonate granulesand moulded directly at normal moulding temperatures. For example 200 mgof TTL was mixed as a dry powder with 500 g of polycarbonate granules(Makroion 2400, supplied by Bayer) and moulded into 1.8 mm thick planolenses at 280° C. The resulting lenses have an optical density of 3.0 at532×10⁻⁹ m. This optical filter absorbs strongly at 532×10⁻⁹ m. Theoptical filter has excellent photostability properties, and consequentlydoes not require the addition of additives such as antioxidants or ultraviolet absorbers, although this may be done if preferred.

In order to show the excellent photostability properties of an opticalfilter according to the present invention, during testing of thematerial it has been found that in an accelerated photofatigue test, TTLshows only a 5.7% loss of absorbance (in polycarbonate) after 800 hours.

By comparison the photostability of PtOEP is very inferior when comparedto TTL. Normally the PtOEP is injection moulded into the polycarbonatehost and in an accelerated photofatigue test it was found that apolycarbonate optical filter incorporating PtOEP showed a 22% loss ofabsorbance after only 18 hours. This loss of absorbance increases to 34%after 66 hours, and 70% after 350 hours.

Other absorbing materials for absorbing other narrow wavelength bandscan be incorporated into the host material together with the TTLmaterial to provide protection against multiple narrow wavelength bands,for example, vanadyl phthalocyanine (VOPc) is suitable for theabsorption of ruby laser wavelength of around 694×10⁻⁹ m. For example 35mg of VOPc was mixed as a dry powder with 500 g of polycarbonate(Makroion 2400 supplied by Bayer) and moulded into 1.8 mm thick planolenses at 280° C. The resulting lenses have an optical density of 2.0 at694×10⁻⁹ m Tris(p-diethylaminophenyl)-aminium hexafluoroantimonate(Tdaha) is suitable for the absorption of neodium laser wavelength ofaround 1064×10⁻⁹ m. 338 mg of Tdaha is mixed as a dry powder with 500 gof polycarbonate (Makroion 2400 supplied by Bayer) and moulded into 1.8mm thick plano lenses at 280° C. The resulting lenses have an opticaldensity of 2.0 at 1064×10⁻⁹ m.

It should be noted that TTL can be incorporated into polymeric matrixhosts other than polycarbonate, for example polyurethane.

We claim:
 1. An optical filter for the absorption of electromagneticradiation in a narrow wavelength band, the filter comprising atransparent host material, and an electromagnetic radiation absorbingmaterial-comprising the compound 5,10,15,20 tetrakis (4methoxyphenyl)-21H,23H porphine palladium (II).
 2. An optical filter asclaimed in claim 1 wherein said host material comprises polymericmatrix.
 3. An optical filter as claimed in claim 2 wherein saidpolymeric matrix comprises polycarbonate.
 4. An optical filter asclaimed in any preceding claim wherein the filter comprises at least onefurther electromagnetic radiation absorbing material for absorbing anarrow wavelength band of radiation.